Equity - Narrative (Details)
 1 Months Ended 3 Months Ended 12 Months Ended
Oct. 25, 2021
USD ($)
Aug. 06, 2020
USD ($)
Jul. 28, 2020
USD ($)
Jun. 11, 2020
USD ($)
$ / shares
shares
Dec. 18, 2019
USD ($)
$ / shares
shares
Jun. 27, 2017
USD ($)
$ / shares
shares
Aug. 31, 2017
USD ($)
Mar. 31, 2021
USD ($)
shares
Mar. 31, 2020
USD ($)
Dec. 31, 2021
USD ($)
vote
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Aug. 31, 2020
$ / shares
Subsidiary, Sale of Stock [Line Items]                          
Issuance of common stock through at-the-market offering, net | $                   $ 51,934,000 $ 2,108,000 $ 1,006,000  
Class of warrant or right, outstanding (in shares)                   10,735,980 12,378,016 31,426,248  
Exercise price (in dollars per share) | $ / shares                   $ 1.62 $ 1.60 $ 1.12 $ 2.54
Warrant liabilities | $                   $ 25,423,000 $ 28,708,000    
Common stock, shares authorized (in shares)                   200,000,000 200,000,000    
Common stock, par value (in dollars per share) | $ / shares                   $ 0.0001 $ 0.0001    
Common stock, shares issued (in shares)                   123,622,965 108,071,249    
Common stock, shares outstanding (in shares)                   123,622,965 108,071,249    
Number of votes per share that common stockholders are entitled to | vote                   1      
Dividends declared or paid on common stock | $                   $ 0      
Warrants to purchase common stock                          
Subsidiary, Sale of Stock [Line Items]                          
Class of warrant or right, outstanding (in shares)                   10,443,511 12,085,547 22,988,501  
Class of warrant or right, number of warrants exercised (in shares)                   1,642,036      
Issuance of common stock upon exercise of common warrants (in shares)                   1,076,669      
At-The-Market Offering                          
Subsidiary, Sale of Stock [Line Items]                          
Sale common stock | $ $ 75,000,000.0           $ 50,000,000.0            
Sale of stock, number of shares issued in transaction (in shares)               1,069,486   13,767,511      
Net proceeds from issuance of common stock | $               $ 2,100,000   $ 51,900,000      
Net proceeds from issuance of common stock | $                   51,958,000 $ 2,108,000 $ 1,006,000  
August 2020 Shelf Registration Statement                          
Subsidiary, Sale of Stock [Line Items]                          
Sale common stock | $   $ 200,000,000                      
SOBI Purchase Agreement                          
Subsidiary, Sale of Stock [Line Items]                          
Sale common stock | $       $ 25,000,000                  
Sale of stock, number of shares issued in transaction (in shares)       5,416,390                  
Share price (in dollars per share) | $ / shares       $ 4.6156                  
Sale of stock, percentage of ten-day volume weighted average price of common stock       120.00%                  
Redemption premium | $     $ 14,500,000                    
December 2019 Financing                          
Subsidiary, Sale of Stock [Line Items]                          
Sale common stock | $         $ 65,600,000                
Sale of stock, number of shares issued in transaction (in shares)         37,634,883                
Share price (in dollars per share) | $ / shares         $ 1.46                
Class of warrant or right, outstanding (in shares)         22,988,501                
Warrant issued | $         $ 40,700,000                
Issuance costs | $                 $ 4,400,000        
Warrant liabilities | $                   25,400,000      
Warrant, decrease in equity, amount | $                   $ (2,300,000) $ (10,400,000) $ (900,000)  
December 2019 Financing | Pre-Funded Warrant                          
Subsidiary, Sale of Stock [Line Items]                          
Class of warrant or right, number of warrants exercised (in shares)         8,342,128                
Exercise price (in dollars per share) | $ / shares         $ 0.0001                
December 2019 Financing | Common Warrant                          
Subsidiary, Sale of Stock [Line Items]                          
Share price (in dollars per share) | $ / shares         0.125                
Exercise price (in dollars per share) | $ / shares         $ 1.46                
Warrants and rights outstanding, term         5 years                
2017 PIPE                          
Subsidiary, Sale of Stock [Line Items]                          
Sale of stock, number of shares issued in transaction (in shares)           2,750,000              
Share price (in dollars per share) | $ / shares           $ 16.00              
Net proceeds from issuance of common stock | $           $ 47,100,000              
Common stock, shares authorized (in shares)                   200,000,000      
Common stock, par value (in dollars per share) | $ / shares                   $ 0.0001      
Springer Purchase Agreement                          
Subsidiary, Sale of Stock [Line Items]                          
Share price (in dollars per share) | $ / shares           $ 17.71              
Springer Purchase Agreement | Common stock                          
Subsidiary, Sale of Stock [Line Items]                          
Issuance of common stock, net of issuance costs (in shares)           338,791              
Warrants to purchase common stock                          
Subsidiary, Sale of Stock [Line Items]                          
Sale of stock, number of shares issued in transaction (in shares)           79,130              
Exercise price (in dollars per share) | $ / shares           $ 17.71              
Warrants and rights outstanding, term           5 years              
Share price (in dollars per share) | $ / shares           $ 0.125